How to Build
a Radio Interface
Using an Arduino Nano



Early in 2016 the Hamvoip group began investigating an alternate means for controlling radios and other external devices using GPIO. The cheap USB FOBS always seemed to be a stumbling block for many hams to modify and it is increasingly hard to find FOBS that do not have potted electronics and are impossible to modify. One thought was using the available GPIO on the Raspberry Pi board but there were concerns about both incoming and outgoing EMI in the RF rich environments that our systems often encounter. So we decided to develop a means of controlling the COS, PTT, and other signals outside of the sound device and also the Raspberry Pi board itself. First tests were with the FTDI series of USB to RS232 (GPIO) devices. There are tons of them on ebay from China at under $5. Unfortunately almost all of the cheap FTDI boards are fake copies and in our tests the bit manipulation does not work properly. A true FTDI board which typically costs $15 or more works fine. Knowing that hams are cheap we started to look at the Arduino Nano boards. Again there are tons of them out there at cheap prices from China (less than $3) but so far they all have worked well. The Nano boards also have the advantage of giving many more bits and also A/D and other serial formats if needed. This howto describes how to build a Nano interface for Allstar using the hamvoip Raspberry Pi 2/3 version 1.5 or greater software.

Parts required

Here is a list of parts I used in the construction of this interface. In most cases there is no requirement that you use these exact parts if you have something equivalent on hand. The only things that you should order as specified is the Nano board and a working (soundwise) USB FOB. Potted FOBS are fine since you do not have to modify them. How you package it is up to you. The photos shown here are my first attempt at building it and this can be considered a prototype unit. The container, how boards are mounted, the connector used to connect to the radio are all things that are user selectable.

Note that the Nano can handle PTT, COS, CTCSS, fan or other control signals for two nodes. This project only shows one. Two sound FOBS and the Nano could be installed in one box with two radio connections.

As of this writing there is a commercial board being designed and tested that would eliminate most of the construction shown here. No price is available yet. Here is a link to that project - More information will be published here and on the hamvoip forum when available.

Photos of the single node Nano Interface.

Both the Sound FOB standard USB and the Nano mini-USB exit from the side and are connected to the Raspberry Pi via adapter cables.

The USB Sound FOB is clamped to the bottom of the case with an aluminum bracket. The Nano is mounted to the top of the bracket with Velcro and some hot glue to hold the board against the case.

Four LED's are mounted on one end with a DB9 as the connector to the radio. The DB9 is wired the same as the Alinico DR-x35 radios. A male to male DB9 cable to the radio would be used in the case of an Alinco radio.

The PTT FET, COS diode, and associated components are mounted directly to the DB9. The two resistors and coupling cap for the audio are mounted at the miniature plug which is inserted into the sound FOB. You have the option of using plugs to connect to the sound FOB or directly wiring by soldering internally to the audio jacks. Leaving the sound FOB in its original case is also optional. However you mount it be sure the push buttons - up/down volume etc. do not become engaged in your mounting process.

All connections to the Nano use push on connectors. They can easily be repositioned to other pins if necessary.

Not shown but there is a "peep" hole on the top side of the case where the USB sound FOB's green (heartbeat) LED can be seen. The FOB is mounted against the top of the case and the hole is positioned over the LED.


The Arduino IDE is used to develop software for the Nano and other Arduino products. It is also used to download the programs to the chip. There are many programming examples given so you can learn a lot just playing. The IDE is NOT needed to use the Nano with Hamvoip Allstar. When available Hamvoip Allstar code will recognize the Nano and download all needed software to make the Nano work as a GPIO interface.


As you all build this project I would like to see your designs, how you package it etc. Send me photos and info and I will include them on this page.

© 2016 - WA3DSP